1. Field of the Invention
The present invention relates generally to methods for drilling and, more specifically, to a method of drilling holes in ductile materials.
2. Description Of the Related Art
It is known to use split-point drills for drilling holes in ductile materials. These split-point drills are commonly used on workpieces of ductile material such as low carbon steel. In conventional drilling, a feedrate of the split-point drill is constant throughout a full drill stroke, followed by a rapid feedrate velocity retraction of the split-point drill. During conventional drilling, material immediately beneath a point of the split-point drill undergoes severe plastic deformation resembling an extrusion process. As the split-point drill nears an exit side of the workpiece, the remaining material is unable to support the cutting forces of the drill and begins to form a mushroom which bulges from the exit side of the workpiece as the drilling operation proceeds. Under conventional drilling, this propagating mushroom becomes a drill cap that is retained on the exit side of the workpiece. Drill caps are thin sections of material which resemble the shape of the drill point. A small push-out burr, in the shape of a cylindrical extrusion, is also created around the perimeter of the drilled hole. As the split-point drill exits the workpiece, the drill cap folds over and hinges along an edge of the drilled hole on the exit side.
Although the above method of drilling has worked well on ductile materials, it suffers from the disadvantage that the drill caps present a difficult challenge for automated deburring. The drill cap often folds back into the drilled hole in conventional mechanical deburring processes (wire brush, vibratory). As a result, the drill cap contaminates deburring media in abrasive flow processes, and its shape and attachment to the workpiece renders other techniques ineffective (e.g., electrolytic).